Signal transmitting system



INPUT OUTPUT INF UT OUTPUT BEST AVAILABLE com,

S. J. BEGUN SIGNAL TRANSMITTING SYSTEM Filed March 26, 1957 5Sheets-Sheet 1 INVENTOR. Begun mixi Jul 18, 1939.

s. .1. BE GUN SIGNAL TRANSMITTING SYSTEM Filed larch 26,

5 Sheets-Sheet 2 INVENTOR.

A QRNEYS.

July 18, 1939. s, E M 2,166,517

smrm. TRANSMITTING sY's'rEl Filed larch 26, 1937 5 Sheets-Sheet 5 INVENTOR.

Semi Begun BY I ATTORNEY.

5 Sheets-Sheet 4 S. J. BEGUN Filed larch 26, 1937 SIGNAL TRANSMITTINGSYSTEI July 18, 1939.

I) l'lnlllllil? Ill bl INVENTOR ATTORNEYS iii ' July 18, 1939. s. J.BEGUN 2,166,517

SIGNAL TRANSMITTING SYSTEM Filed March 26, 1937 5 Sheets-Sheet 5 7 SMICFI a *35 1 I INVENTOR. V Semi I B an 'I'TORNEYS .7 TFL-EPHONY.

Patented July 18, 1939 UNITED STATES Exams-e" 2,166,517 PATENT OFFICE2,166,517 SIGNAL TRANSMITTING SYSTEM Semi J. Begun, New York, N. Y.,minor, by mesne assignments, to Carl] Tucker, New York.

Application March 26. 1937, Serial No. 133,144

34 Claims.

This invention relates to improvements in electrical signal transmittingsystems.

The basic object of this invention is to provide improved forms oftransmission circuits between transmitting and receiving apparatus toinsure a maximum of dependability of such systems.

A further object of the invention is to provide a transmission system ofthis nature in which the signal energy level is not reduced toimpractical and inoperative values upon the development of a shortcircuit or an open circuit on the transmission line.

These and many more detailed and specific objects of the invention willbecome apparent to those skilled in the art from the followingdescription when taken in connection with the attached drawings.

This invention resides substantially in the combination, construction,arrangement and relative location of parts, all in accordance with thefollowing disclosure.

In the accompanying drawings:

Figure 1 is a diagrammatic illustration of one form of the inventionemploying conductive coupling between the transmission line and thetransmitting and receiving apparatus;

Fig. 2 is a diagrammatic illustration of a modified form of systememploying inductive coup Fig. 3 is a diagrammatic illustration of amodified form of the circuit of Fig, 2 including signaling means forindicating open circuits and short circuits on the transmission line;

Fig. 4 is a diagrammatic illustration of an inductively coupled systemas modified for use with a plurality of signal responsive devicessupplied from a single transmitting source;

Fig. 5 is a diagrammatic illustration of a further modified form of theinvention illustrating the use of double conducting loops;

Fig. 6 is a diagrammatic illustration of an extended form of the systemof Fig. 5 employing two sets of conductive loops; v

Fig. '7 is a diagrammatic illustration of a modification of the systemof Fig. 6; and

Fig. 8 is .a diagrammatic illustration of another method of coupling aplurality of loops to a single transmitter to accomplish the objects ofthis invention. V

A further object of this invention is to provide improved forms ofelectrical signal energy transmission circuits which are highlydependable in that short circuits and open circuits on the transmissionline do not have the effect of reducing the signal energy level in thetransmission line to a point where the signal responsive apparatus isrendered inoperative. There are many fields of use for transmissionsystems having such desirable characteristics. For example,

such a system is of great value on shipboard where even under the normaloperating conditions it is extremely diflicult to keep the transmissionlines for signaling apparatus in good physical condition. Furthermore,under emergency conditions such transmission systems are often subjectedto physical disturbances even to the extent of interruption, therebyrendering the very apparatus which is so vital in emergenciesinoperative. Any improvement in such signaling systems whereby thedependability thereof is increased is of major importance in this fieldof use.

It will be apparent from the following disclosure that the inventionherein disclosed is of course not limited to use on shipboard but may beemployed in any place where it is desired to effect communicationbetween spaced points.

For the eflicient transmission of signal energy in an electricalcommunication system and especially where the system is used as a safetydevice, it is not satisfactory to employ a transmission circuitcomprising one conductor and ground or two conductors between thetransmitter and receiver. The operability of such a system dependsdirectly upon the physical condition of the transmission line and ashort circuit of this conductor to ground in the first instance, or ashort circuit between both conductors in the second instance, or an opencircuit in both instances would render the system inoperative. bility ofsuch disturbances of the physical condition of transmission lines,especially under emergency conditions, renders these forms oftransmission circuits unavailable as part of a safety system.

Where a closed grounded loop transmission line is employed, so long asonly one open circuit occurs the signal energy will reach the receiversince the signal is transmitted thereto over both legs of the loop.However, a loop circuit of this type is no longer satisfactory when onepoint thereof is grounded.

Such loop systems may however be adapted to the purposes of thisinvention as illustrated for example in Figure 1. The system hereillustrated is in connection with a so-called talk-back arrangement,that is to a two-way communication system which makes it possible totalk to each end of the line from the other.

as a loud speaker. which can also be used as is known, as a transmitter,connected to ground at one terminal and at the other terminal to themid-point of a pair of resistances 9 and ill. The other ends of theseresistances are connected by the conductors 5 and 6 to the ends of asecond pair of resistors l and 8, which in turn are connected together.At 4 is diagrammatically illustrated an amplifier having input andoutput The possi- As shown, the sysr tem comprises a signal responsivedevice I, such terminals as indicated. A pair of double-poledouble-throw switches are provided and arranged for-simultaneousoperation by means of a single operating member 3, as diagrammaticallyillustrated. In the normal position of this switch,

at which time the signal responsive device 1 acts a as a transmitter,the input of the amplifier is connected between ground and the commonterminal of the resistances l and 3. At the same time the terminals ofthe device 2 are connected to the output of the amplifier as shown. Bymeans of the operating member 3 the switches may be moved to their otherposition to reverse the connections in an apparent manner, so that thetransmitter l becomes a-receiver or signal responsive device, and thedevice 2 becomes a transmitter and is connected between ground and theinput of the amplifier as is apparent from the figure. At the same timethe transmission line is connected between ground and the output of theamplifier. The amplifier of course is designed to provide the necessaryenergy gain to effect efficient operation of the apparatus. It isdesirable of course that the resistances I, 8 and 9, Ill be of equalvalue. By the proper selection of the value of the resistances l, 8, 9and ID, the drop in energy level upon the occurrence of an open circuitor a short circuit to ground on either conductors 5 and '8 will notresult in such a reduction in the energy level as to render the systeminoperative. However, such an arrangement is not as satisfactory as itis possible to attain. To emphasize this, it is noted that if theassumption is made that the resistances 1, 8, 9 and ID are zero or verylow in value, the result is the same as in the ordinary looptransmission system, and a short circuit would render the systeminoperative. If, on the other hand. the value of these resistances ismade very high. or even infinite, it is apparent that the energy losseswould be so great as to render the system impractical. However, if theimpedance of the receiver and transmitter compared with the impedance ofthe resistors is relatively low. an open circuit or a short circuitwhile diminishing the signal level an undesirable amount, would notrender the system inoperative for some uses.

A much more effective system employing a double conductor or loop systemis illustrated in Fig. 2. In this case the device I (used either as atransmitter or receiver) is connected in series to what may be termedfor the moment the secondaries of a pair of transformers 9 and 10. Theprimaries are connected in series to the conductors 5 and 5 and havetheir common terminal grounded. The other ends of the conductors 5 and 6are connected to what for the moment may be termed the secondaries ofthe transformers 1 and 8', the common terminal of which is grounded.shunted across the secondaries of transformers 1' and 8' are theresistances II and I2 and similarly the resistances l3 and I4 areshunted across the primaries of transformer 9' and [0. As before anamplifier which it may be noted can be of the vacuum tube multi-stagetype, is diagrammatically illustrated at 4, and having the input andoutput terminals as shown. As before, a pair of double-pole,double-throw switches with a common operating member 3 are employed, andthe device 2 (which may be used either as a transmitter or a receiver)is connected when the switches are in the position shown to the outputof the amplifier. The primaries of transformers 'I' and 8 are connectedin series by means of the switch 3 in the position 8' and thesecondaries of transformers 9' and i 0' be connected so that theconductors 5 and 6 are at the same potential and of the same polarity.

To fully appreciate the operation of this system some characteristics ofan ideal transformer should be reviewed. If the primary of such atransformer is considered as a load in any circuit while the secondaryis open, it is well known that the primary has the characteristic of apure reactance. If the secondary is short circuited and the couplingbetween the primary and secondary is close, this short circuit reflectsback to the primary and the primary can therefore be considered as beingshort circuited. Advantage is taken of this characteristic of atransformer in the system of this invention.

To understand the operation of this system it will be first assumed thatthe resistances ll, l2,

I3 and II are not employed. If conductor 5 is grounded the windings oftransformers 1' and 9' connected thereto are short circuited and as aresult the other windings thereof are in effect short circuited. Byproperly matching the impedance of the transmitter and receiver thiswould produce no noticeable loss in transmission. A similar resultoccurs if conductor 6 is grounded. However, if conductor 6 for anyreason is open circuited the windings of transformer 8' and I0 connectedthereto will not be loaded and the other windings of these transformerswill have considerable impedance, resulting in a consider- .able loss ofenergy transmitted over the other conductor through the transformers 8'and i0.

However, if the resistances H, I2, I3 and H are connected in circuit asshown in Fig. 2, the above described difficulty in connection with opencircuit on either conductor disappears. If, for example, conductor 5 is"open circuited, the resistances II and I3 across the windings oftransformers 1 and 9 connected to conductor 5, provide loads thereon sothat the other windings thereof are not in effect open circuited, andthere is not such a noticeable loss in energy. A similar result occursif conductor 6 is open circuited. While it is true that the use of theseresistances results in some loss in transmission, the advantage gainedunder the circumstances described above overweigh the disadvantages ofthese losses. By employing resistances of the proper value it ispossible to keep the amplitude of the current in the network being fedto the receiver between extremely narrow limits.

Since a communication system of this type depends, in order to afford ahigh degree of safety, upon the physical condition of the transmissionline, it would be normally desirable and even nec-v essary to keep theircondition under constant check. Therefore, in accordance with thisinvention special means have been provided which will immediatelyindicate if an open or a short circuit occurs anywhere on the line. Inthe arrangement of Fig. 3 there is shown a system which not onlyimmediately indicates an open or short circuit on either transmissionline 5 or 6, but if an open circuit occurs on either line it immediatelygrounds the windings of the transformers connected thereto. Thus inaddition to signaling the condition of the lines, the arrangement ofFig. 3 has the advantage that the windings on open circuit may beloaded, while during normal operation they are not shuntedbyresistances, and hence the losses due to them are not present. In thesystem of Fig. 3 only those windings of transformers 1', 6', 3' and IDare shown as are directly connected to the conductors and 6, since theother portions of the system remain the same as that shown for examplein Fig. 2. The relays l2, I3 and II are connected in series with theconductors 5 and 6 through battery IS. The switches I6, |1, 2| and 22operated by the relays H, |2, Hi and I4 respectively are operated undernormal conditions of the network so that switches l6 and H are closedand switches 2| and 22 are open. To get this result the switches I6 andI1 are manually closed thereby energizing all of these relays, resultingin the holding of switches l6 and H closed and switches 2| and 22 open.Connected between ground and the midpoint of battery I5 is a relay l8which controls a switch IS in series with a grounded signal lamp and agrounded battery. Under normal conditions when there are no shortcircuits on the conductors 5 and 6 this relay I8 is not energized. Whena short circuit occurs on either conductor to ground, relay I8 isenergized. For example, if conductor 5 becomes grounded current flowsfrom it through switch l1, relay I2, right hand portion of battery l5,and relay |8 to ground. This closes switch I9 and completes a circuitfor the signal lamp 20which remains energized until the short circuit isremoved.

During the time that relays H and I2 are energized switch 23 is open.This switch involves a pair of contacts as shown, each respectivelyconnected to one terminal of each of relays 25 and 26 respectively,which in turn are connected at their other terminals to the lines 5 and6. Relay |3 in addition to controlling switch 2|, controls switches 30and 33 which are respectively open and closed when this relay isenergized as it normally is. In the same way relay I4, in addition tocontrolling switch 22, controls switchcs 29 and .34 which arerespectively closed and open when the relay I4 is energized as itnormally is. Relay 25 controls the switches 28, 3| and 35 and relay 26controls the switches 21, 32 and 36, all of which switches are in theposition shown since the relays 25 and 26 are de-energized as theynormally are. If conductor 5 should become open circuited, relays II andI2 will be deenergized, so that switch 23 closes connecting the battery24 to relay 26 through ground over conductor 6, relay l4 and switch 2|.Relay 25 will not operate. however. since conductor 5 is open circuited.The operation of relay 26 will close switch 21, open switch 32, andclose switch 36. The closing of switch 21 will be a short circuit acrossthe winding of transformer 1' connected to conductor 5 through theclosed switch 28. The closing of switch 36 will connect the signal lamp31 through the battery to ground, energizing this device and signalingthe presence of an open circuit. At the time that the open circuitoccurred on conductor 5, relays l3 and (4 were de-e'nergized so thatswitches 2| and 22 closed. The de-energization of relay |3 causes switch33 to open and switch 30 to close. Switches 29 and 30 being closed, puta short circuit on the winding of transformer 9' connected to conductor5. Thus there is substantially no diminution in the energy going overconductor 6 because the shown windings of transformers 1' and 9' areshort circuit through ground, reflecting this short circuit back totheir associated windings. The signal lamp 31 remains energized untilthe open circuit of conductor 5 is eliminated. The condensers 36, 33, 40and 4| LAU-ILHJ are employed as blocking condensers to prevent the flowof the D. C. current of these signal and control circuits frompassingthrough the windings of the transformers. With this system itwill be seen that under normal operating conditions there is no directcurrent flowing to ground which is especially important on shipboard inorder to avoid the difliculties of electrolysis.

As will be apparent to those skilled in the art, a quite similaroperation of the system occurs through the other sets of contacts andrelays when an open circuit occurs on conductor 6. In this case thesignal light 31 is energized as before, and short circuits are putacross the shown windings of transformers 8' and In.

It will be apparent to those skilled in the art that different relayarrangements may be employed for accomplishing the same results. Theimportant advantage of this arrangement is that it eliminates thenecessity for load resistances constantly connected across thetransformer windings, as is required by the system of Fig. 2. It is tobe noted that this arrangement is capable of two-way communication inaccordance with the disclosure in Fig. 2, since the amplifier, switchmechanism, transmitters and/or receivers may be connected to the otherwindings of the transformers in the manner shown in Fig. 2. It isimportant to note that all of the various connections to the relays andcontrol devices, as well as the devices themselves may be all enclosedin a single compact unit so that the danger of injury to the controlcircuits is minimized. These units would be concentrated at thetransmitting and receiving stations, and would not. as appears from Fig.3. have physical lengths comparable to the lengths of the conductors 5and 6.

There is shown in Fig. 4 one way communication system employing theprinciples of this invention. At 42 is a microphone connected to theinput of the amplifier 43. The output terminals of this amplifier areconnected to the primary windings of the transformers 44 and 45. The

secondaries of these transformers have a common In each case thesecondaries are connected in series to the signal responsive devices 56,51 and 58. It is first to be noted that by reason of the connectionsbetween the windings of the transformers so that conductors are all ofthe same potential with respect to ground, a short circuit will producelittle or no effect. If either conductor 5 or 6 is open circuited theload resistances 46, 41, 46 and 49 will prevent a complete open circuiton the primary windings of the transformers, so that substantially thesame amplitude of energy will travel to the loud speakers over the otherconductor. With this system the only way that a loud speaker can becompletely out out is to have an open circuit on the branch conductorextending to the associated transformers from either conductor 5 or 6.With both ends of the feeding lines shunted with the resistance bridgesas shown, the load due to these resistances will be relatively smallerthe more speakers there are connected in circuit. In other words, theresistances employed may be of the same order of value as theresistances employed for example in the circuit of Fig 2 with only onespeaker, regardless of the number of loud speakers employed in thesystem of Fig. 4. This represents the minimization of losses due to thepresence of the resistors. If these resistors were duplicated for eachloud speaker a considerable loss would result. This connection ofresistances results in the fact that their value depends only upon howmuch volume reduction is permissible for the speaker unit most effectivefor an open circuit of either conductor between the last unit of theresistance bridge and the one preceding it. Thus this system is capableof operation at high efficiency and it is not necessary to providespecial means to ground the conductors when they are open circuited asin the case of the two-way communication system of Fig. 3.

It is highly desirable in all of the systems disclosed herein to placethe conductors 5 and 8 as far apart as possible, for example onshipboard these conductors can be run on opposite sides of the ship.However, in many cases it is not possible or desirable to physicallyspace these conductors, but it is preferable to have them closetogether, as for example in the same cable. Under these conditions themanner of reversely connecting the windings of the transformers as shownin Fig. 4 is of practical value because these conductors are then at thesame potential. Being at the same potential a short circuit therebetweenwill not affect in any way the transmission of signal energy.

The system of Fig. 5 shows the application of the principle of thisinvention to a pair of feeding loops used for transmitting the signalenergy. The amplifier diagrammatically illustrated at BI is providedwith the output transformers of which the secondaries 62 and 83 areshown connected in series and grounded at the common point. Their otherterminals are connected respectively to the loops 5 and 8' at the commonterminal of the blocking condensers 88, 81, 68 and 88. The primaries 62and 88 are again connected so that the two loops are at the samepotential. These loops are interconnected as shown by means of animpedance 18. The loud speakers 1| are connected to the secondaries oftransformers l2 and 18 which secondaries are connected in series asshown. The primaries of these transformers are connected in seriesbetween the network through blocking condensers l4 and I5 and have theircommon terminal grounded as shown. As many of these speaker units may beapplied between the loops as desired. At 16 and 11 are a pair of relaysconnected in series through a battery I8 across the loops in the mannershown. The midpoint of the battery is connected to ground through thewinding of relay l8. Relay 18 controls switch 88 and relay 11 controlsswitch 8|. The fixed contacts of these switches are connected togetherand to ground through the signal device 82. The movable contacts ofthese switches are connected together and to ground through will notinterfere with the operation of the loud speakers for the reasonspointed out in connection with the system of Fig. 2 for example where inthis respect the transformer connections to the conductors are the same.The short circuit on one conductor will result in the flow of currentover the other conductor to the connected primaries of the speakertransformers with substantially no diminution.

The occurrence of an open circuit on either or both of the loops willlikewise not interfere with the operation of the loud speaker devicesbecause the current flows to their transformers over each loop in bothdirections. Obviously, therefore, an open circuit will not interferewith the arrival of current at the transformers. Signal devices areprovided, however, to indicate the occurrence of short circuits or opencircuits. Under normal operating conditions relays l6 and H arecontinuously energized from battery 18 through the loops and the chokecoil 88. This choke coil is proportioned to prevent the interfiow ofsignal current. Thus switches and 8| are open and signal device 82 isdeenergized. Switch 84 is also open since the relay I8 is energized.Upon the occurrence of an open circuit on either conductor the relays l6and 11 will be de-energized, closing switches 88 and 8| and connectingthe signal devices 82 through the battery 83 to ground. Thus thepresence of the open circuit is indicated. If a short circuit to groundoccurs on either conductor, current will flow from ground through theshort circuited loop, through either relay 16 or 11, depending uponwhich is connected to the short circuited loop, through the battery l4and to ground through the relay 18. The result is that switch 84 willclose and the signal loop 85 will be connected through the battery 83 toground. Thus a short circuit on either loop to ground is indicated. Thetwo relays l6 and 11 can obviously be replaced by a single relay inseries with an impedance of equal value to maintain the A. C. balance ofthe loops.

Figs. 6 and 7 disclose systems employing two different independentdouble loops to feed a number of receiving units. Each loop has anindependent control arrangement to indicate open circuits or a groundedcondition of one or the other conductors of the loop pairs. The relayarrangement illustrated for each pair of loops is the same as thatdescribed in full detail in Fig. 5. The loud speakers are connected tothe loops in the same way. For this reason the control arrangements andthe speaker operation will not be described since each pair of loopsoperates in the same way as the arrangement of Fig. 5.

The feature of the system of Fig. 6 is in the manner in which theamplifier is coupled to the two loops so that if by chance both channelsof one pair of loops becomes grounded this will have no effect upon theoperation of the other pair of loops. The output of the amplifier isconnected to the primaries of four transformers 80, 8|, 82 and 83. Theprimaries of transformers 80 and 8| are connected in series through theresistances 84 and 85 to the output of the amplifier and in parallelwith the primaries of transformers 82 and 83, which are connected inseries with the resistances 88 and 81. The primaries are connected asindicated so that the potentials of both leads of each pair are thesame. The secondaries of transformers 80 and 8| are connected in serieswith each other and with the resistances 88 and 88 across the two loops8' and 5' of one pair. In a similar way the secondaries of transformers82 and 93 are connected in series with resistances I and IN across thetwo loops "and 5" of the other pair. The common terminal of each pair ofsecondaries is grounded as shown.

The resistances are all selected to have a value so that if both loopsof one pair should become grounded the impedance unbalance thus causedwill not be reflected back into the output of the amplifier to such anextent as to prevent useful transmission of energy over the loops of theother pair.

It is of course apparent that the number of pairs of loops may beincreased by duplication and by connecting them in parallel to theoutput of the amplifier. Thus a short circuit to ground on both loops ofany pair is not reflected back in any substantial manner to interferewith the operation of the loops of all the other pairs.

Since resistances or impedances as described in the arrangement of Fig.6 involve a constant energy loss which it is desirable to eliminate, thesystem of Fig. '7 has been developed. In this arrangement as before, thetwo pairs of loops, the manner of connecting the loud speakers thereto,and the signaling circuits for indicating open circuits and shortcircuits are the same. The system of this figure differs in that adifferent method is illustrated for connecting the output of theamplifier with the pairs of loops without employing impedances toprevent the reflection back to the amplifier of short circuits of bothloops of a pair to ground. In this case the output terminals of theamplifier I are connected to the primaries in series of a pair oftransformers I02 and I03. The secondaries of these transformers areconnected in series with the primaries of the four transformers I04,I05, I06 and I 01. The secondaries of these four transformers areconnected in pairs in series to the loops 5 and I5 and 5" and I5",respectively as shown. The common point of these secondaries isgrounded. If both loops for example 5" and 6" of one pair should beaccidentally grounded. the secondary space of the transformers I06 andI0! can be considered as short circuited. This short circuit willreflect back to transformer I03, which is properly matched in impedanceto the output impedance of the amplifier so that the output energy ofthe amplifier will be transferred to the transformer I02 and onto theother pair of loops. With this arrangement the energy level in the otherpair of loops will be higher than the normal energy level when bothloops are operated.

The advantage of this system over that of Fig. 6 is that there is noenergy loss due to the presence of impedances corresponding to theimpedances 94 to WI inclusive. This transformer arrangement of Fig. 7can be used for more than two pairs of loops by simply paralleling theadditional pairs to the output of the amplifier.

The control apparatus for operating the signal lights 82 and 85 is thesame as that shown in Figs. 5 and 6. and therefore has been indicated inFig. 7 diagrammatically by a square and the symbol It is againworthwhile noting that with systems of this type. especially when usedon shipboard the different types of loops may be spacially distributedover different parts of a ship so that any physical damage to one pairis less likely to simultaneously occur on the other pairs.

Fig. 8 illustrates another transformer arrangement for coupling theoutput of the amplifier to three or more output circuits such as thepairs of loops previously discussed, In this case the primaries 202, 203and 204 of three transformers are connected in series to the output ofthe amplifler I. The secondaries thereof are connected respectively inseries with the primaries of the pairs of transformers 205 and 206, 201and 208, and 209 and 2 I 0. The secondaries of these transformers areconnected in series in pairs with their common terminal grounded. Theirremaining terminals are respectively connected to the output circuits,the remainder of which may be of any form such as that shown for examplein Fig. 5. The short circuit to ground of both loops of each pairconnected to the independent pairs of secondaries of the arrangement ofFig. 8 will not be reflected back to the output of the amplifier tointerfere with the operation of the other loops.

The arrangement of Fig. 8 lends itself to selective operation of aplurality of transmitting loops. Thus, for example if pairs of loops areconnected to the leads of each of the pairs of secondaries in accordancewith the system of Fig. 5. and double contact grounding switches SM, 302and 330 are connected across the loop supply leads, then it is possibleby closure of one or more of these switches to intentionally ground theloop associated wherewith as distinguished from accidental grounding.Thus, for example. if switch 30I is closed both of the leads of thesecondaries of the associated transformers are directly grounded, withthe result that that transmitting loop connected thereto isshort-circuited and none of the signal responsive devices connected tothat loop are operated. All the signal energy. however, is thendistributed as explained in the case of accidental ground to the otherloops through the other transformers. This simple arrangement provides asafe and dependable method of selected operation of a plurality of loopsfrom a single signal source. An advantage of this ai rangement is thatif anything goes wrong with the short circuiting switches, as forexample if the contacts thereof are guarded, the worst that could happenis that the signal responsive devices of the connected loop willcontinue to operate. which of course is not as serious as a failureinvolving inoperativeness of the equipment;

It is of course apparent to those skilled in the art that instead ofusing manually operated grounding switches that remotely controlledmechanical or electromagnetic switches or relays may be employed.

It will be apparent to those skilled in the art that with the looparrangement as disclosed. the pairs of loops may be multiplied so as toreduce the number of loud speaker or receiver units connected to eachpair, thereby minimizing the number of speakers or receivers which aredisabled if one pair of loops go out of service, with the gen eralresult of greatly increasing the overall safety of the system.

It is noted in connection with these systems, and especially byreference to Fig. 4. that it is desirable to wind the secondaries of thetransformers 50 and 5|, 52 and 53, and 54 and 55 to have a directcurrent resistance of about 4 ohms when the A. C. impedance of the voicecoil, for example, of the loud speakers is 12 ohms. With thisarrangement a direct short circuit of the voice coil to any one speakerwill not be reflected back to the conductors 5 and 8 to interfere withthe operation of the other loud speakers in any manner.

It is hardly necessary to note that in some installations instead ofactually connecting the socalled grounded terminals to ground, they mayall be interconnected by a conductor of the proper electricalcharacteristics.

From the above description it will be apparent to those skilled in theart that the principles of this invention may be applied in a practicalsense in a wide variety of arrangements. I do not, therefore, desire tobe strictly limited to this disclosure as given for purposes ofillustration, but rather to the scope of the appended claims.

What is claimed is:

l. A talk-back signaling system comprising an amplifier, a pair ofcombined transmitter-receivers, a transmission line comprising a pair ofconductors, impedances connecting the conductors together at theirrespective ends, means connecting one of said transmitter-receivers tothe impedance at one end of the line, and switching means for connectingthe impedance at the outer end of the line to the output or input of theamplifier and the other transmitter-receiver to the input or the outputof the amplifier.

2. In a signaling system the combination comprising a source of signalenergy, a signal responsive device, a transmission line comprising apair of conductors, two pairs of transformers, one set of responsivewindings of each pair being connected in series across the respectiveends of the conductors, means for grounding the common terminal of eachpair of windings, an impedance shunted across each of said windings, theother set windings of each pair of transformers being respectivelyconnected in series, one set to the signal source and one set to thesignal responsive device.

3. In a talk-back signal transmission system the combination comprisingan amplifier, a pair of transmitter-receivers, a transmission linecomprising a pair of conductors, a pair of transformers, the respectivewindings of each pair being connected in series across the respectiveends of the conductors, the common terminal of each pair of windingsbeing grounded, impedances shunted across each of said windings, theother winding of one pair of transformers being connected in series toone transmitter-receiver, and means for connecting the other pair ofwindings of the other pair of transformers alternately to the output andinput of the amplifier and the other transmitter-receiver alternately tothe input and output of the amplifier.

4. In a signaling system the combination comprising a source of signalenergy, a signal responsive device, a transmission line comprising apair of conductors, two pairs of transformers, one set of respectivewindings of each pair being connected in series across the respectiveends of the conductors, means for grounding the common terminal of eachpair of windings, a resistance shunted across each of said wind ngs, theother set windings of each pair of transformers being respectivelyconnected in series, one set to the signal source and one set to thesignal responsive device.

5. In a talk-back signal transmission system the combination comprisingan amplifier, a pair of transmitter-receivers, a transmission linecomprising a pair of conductors, a pair of transformers, the respectivewindings of each pair being connected in series across the respectiveends of the conductors, the common terminal of each pair of windingsbeing grounded, resistances shunted across each of said windings, theother winding of one pair of transformers being connected in series toone transmission-receiver, and means for connecting the other pair ofwindings of the other pair of transformers alternately to the output andinput of the amplifier and the other transmitter-receiver alternately tothe input and output of the amplifier.

6. In a signaling system the combination comprising a source of signalenergy, a signal responsive device, a transmission line comprising apair of conductors. means for coupling the signal source and thereceiver to the respective ends of both conductors, said meanscomprising pairs of transformers at the respective ends of thetransmission line having the respective windings of the pairs connectedto the ends of the conductors, impedances shunting said windings, and acommon grounding connection for the impedance and associated winding.

7. In a signaling system the combination including a transmission linecomprising a pair of conductors, impedances shunted across therespective ends of the conductors, said impedances having anintermediate point grounded, a signal source coupled to the impedance atone end of the line, a signal responsive device coupled to theimpedances at the other end of the line, and means connected to saidconductors for signaling the grounding of either conductor or the opencircuiting of either conductor.

8. In a signaling system the combination including a transmission linecomprising a pair of conductors, impedances shunted across therespective ends of the conductors, said impedances having anintermediate point grounded, a signal source coupled to the impedancesat one end of the line, a signal responsive device coupled to theimpedances at the other end of the line, and means for connecting aresistance across the portions of the impedances connected to aconductor when it is open circuited.

9. In a signaling system the combination including a transmission linecomprising a pair of conductors, impedances shunted across therespective ends of the conductors, said impedances having anintermediate point grounded, a signal source coupled to the impedancesat one end of the line, a signal responsive device coupled to theimpedances at the other end of the line, means for connecting aresistance across the portions of the impedances connected to aconductor when it is open circuited, and means for signaling thegrounding or open circuiting of either conductor.

10. In a signaling system the combination including a transmission linecomprising a pair of conductors, a pair of impedances shunted, in

series across the respective ends of the conductors, the common terminalof each pair of irnpedances being grounded, a source of signal energycoupled to the impedances at one end of the line, a signal responsivedevice coupled to the impedances at the other end of the line, andsignaling means interconnecting the conductors for indicating thegrounding of either conductor.

11. In a signaling system the combination in cluding a transmission linecomprising a pair of conductors, a pair of impedances shunted in seriesacross the respective ends of the conductors, thecommon terminal of eachpair of impedances being grounded, a source of signal energy coupled tothe impedances at one end of the line, a signal responsive devicecoupled to the impedances at the other end of the line, and signalingmeans interconnecting the conductors for indicating the open circuitingof either conductor.

79. TFLEPHDNY- 12. In a signaling system the combination including atransmission line comprising a pair of conductors, a pair of impedancesshunted in series across the respective ends of the conductors, thecommon terminal of each pair of impedances being grounded, a source ofsignal energy coupled to the impedances at one end of the line, a signalresponsive device coupled to the impedances at the other end of theline, and signaling means interconnecting the conductors for indicatingthe grounding of either conductor.

13. In a signaling system the combination including a transmission linecomprising a pair of conductors, a pair of impedances shunted in seriesacross the respective ends of the conductors, the common terminal ofeach pair of impedances being grounded, a source of signal energycoupled to the impedances at one end of the line, a signal responsivedevice coupled to the impedances at the other end of the line, and meansconnected between said conductors for placing a short circuit across theportions of said impedances connected to a conductor when it is opencircuited.

14. In a signaling system the combination including a transmission linecomprising a pair of conductors, a pair of impedances shunted in seriesacross the respective ends of the conductors. the common terminal ofeach pair of impedances being grounded, a source of signal energycoupled to the impedances at one end of the line, a signal responsivedevice coupled to the impedances at the other end of the line meansconnected between said conductors for placing a short circuit across theportions of said impedances connected to a conductor when it is opencircuited, and means connected between said conductors for indicatingthe grounding of either conductor.

15. In a signaling system the combination including a transmission linecomprising a pair of conductors, a pair of impedances shunted in seriesacross the respective ends of the conductors. the common terminal ofeach pair of impedances being grounded, a source of signal energycoupled to the impedances at one end of the line, a signal responsivedevice coupled to the impedances at the other end of the line, meansconnected between said conductors for placing a short circuit across theportions of said impedances connected to a conductor when it is opencircuited. and means connected between said conductors for indicatingthe open circuiting of either conductor.

16. In a signaling system the combination including a transmission linecomprising a pair of conductors, a pair of impedances shunted in seriesacross the respective ends of the conductors, the common terminal ofeach pair of impedances being grounded, a source of signal energycoupled to the impedances at one end of the line, a signal responsivedevice coupled to the impedances at the other end of the line, meansconnected between said conductors for placing a short circuit across theportions of said impedances connected to a conductor when it is opencircuited, and means connected between said conductors for indicatingthe grounding of either conductor.

1'7. In a signaling system the combination comprising a source of signalenergy, a transmission line comprising a pair of conductors, a pair oftransformers having their respective windings connected in series, onepair being con- Examiner nected to the output of the signal source andends of said conductors, the common terminal of said last windings beinggrounded, a pair of impedances shunted across said conductors by spacedpoints and grounded intermediate the ends thereof, a plurality of signalresponsive devices and transformers for coupling each of said devices tothe conductors between said impedances, one pair of windings of eachtransformer being connected in series to the associated signalresponsive device and the other pair of windings of each transformerbeing connected in series between the conductors and having their commonpoint grounded.

18. In a signaling system the combination comprising a source of signalenergy, a transmission line comprising a pair of conductors, a pair oftransformers having their respective windings connected in series, onepair being connected to the output of the signal source and the otherpair being connected to the respective ends of said conductors, thecommon terminal of said last windings being grounded, a pair ofimpedances shunted across said conductors by spaced points and groundedintermediate the ends thereof, a plurality of signal responsive devicesand transformers for coupling each of said devices to the conductorsbetween said impedances, one pair of windings of each transformer beingconnected in series to the associated signal responsive device and theother pair of windings of each transformer being connected in seriesbetween the conductors and having their common point grounded, thedirect current impedance of the windings connected to the signalresponsive devices being substantially equal to the impedance of thesignal responsive devices.

19. In a signaling system the combination comprising a plurality ofindependent transmitting networks, a source of signal energy, aplurality of transformers having their primaries connected in serieswith the output of the signal source, the secondaries of eachtransformer being connected in series with the primaries of a pair oftransformers, the secondaries of each pair of transformers beingconnected in series and to the network.

20. In a signaling system the combination comprising a plurality ofindependent transmitting networks, a source of signal energy, aplurality of transformers having their primaries connected in serieswith the output of the signal source, the secondaries of eachtransformer being connected in series with the primaries of a pair oftransformers,thesecondariesof each pair of transformers being connectedin series and to the network and having their common terminals grounded.

21. In a signaling system the combination comprising a plurality ofindependent transmitting networks, a source of signal energy, aplurality of transformers having their primaries connected in serieswith the output of the signal source. the secondaries of eachtransformer being connected in series with the primaries of a pair oftransformers, the secondaries of each pair of transformers beingconnected in series and to the network and having their common terminalsrounded, and grounded signal responsive devices connected to thenetwork.

22. In a signaling system the combination comprising a source of signalenergy, a pair of conductors each forming a closed loop, means forconnecting the source of signal energy between each of said loops andground, and a plurality of signal responsive devices connected betweeneach of said loops and ground.

23. In a signaling system the combination comprising a source of signalenergy, a pair of conductors each forming a closed loop, means forconnecting the source of signal energy between each of said loops andground, a plurality of signal responsive devices connected between eachof said loops and ground, and means for indicating either a shortcircuit to ground on either loop or an open circuit on either loop.

24. In a signaling system the combination comprising a. source of signalenergy including a pair of transformers, a pair of conductors eachforming a closed loop, the secondaries of said transformers beingconnected in series and having their common point grounded, connectionsin the other terminals of the secondaries to the respective loops, aplurality of signal responsive devices and a pair of transformers forcoupling each signal responsive device to said loops, said last pair oftransformers having their primaries connected in series between theloops and their common terminal grounded, and their secondariesconnected in series with the signal responsive devices.

25. In a signaling system the combination comprising a source of signalenergy including a pair of transformers, a pair of conductors eachforming a closed loop, the secondaries of said transformers beingconnected in series and having their common point grounded, connectionsin the other terminals of the secondaries to the respective loops, aplurality of signal responsive devices and a pair of transformers forcoupling each signal responsive device to said loops, said last pair oftransformers having their primaries connected in series between theloops and their common terminal grounded and their secondaries connectedin series with the signal responsive devices. and means connected to theloops for indicating either a short circuit or an open circuit on eitherloop.

26. In a signaling system the combination comprising a source of signalenergy, a pair of networks each comprising two closed conductive loops,a plurality of signal devices interconnected between each of the loopsand ground, transformer means for coupling the source of signal energybetween each of the pairs of loops and ground, and means for preventingthe reflection of open circuits on either loop of each pair back to thesignal source.

27. In a signaling system the combination comprising a source of signalenergy including an amplifier, a pair of networks each comprising twoclosed conductive loops and transformer means for coupling the output ofthe amplifier with each network, said transformer means comprising apair of transformers having their primaries connected in series with theoutput of the amplifier, two pairs of transformers having theirprimaries connected in series with the secondaries of said pair oftransformers, and their secondaries connected in series across the loopsof the respective pairs and having a common ground.

28. In a signaling system the combination comprising a source of signalenergy including an amplifier, a pair of networks each comprising twoclosed conductive loops and transformer means for coupling the output ofthe amplifier of said pair of transformers and their secondariesconnected in series across the loops of the respective pairs and havinga common ground, the signal responsive devices being connected to thepairs of loops each by pairs of transformers having their primariesconnected in series across the loops of the respective pairs with acommon ground and their secondaries connected in series with the signalresponsive devices.

29. In a system for selectively supplying energy from a signal source toa plurality of transmitting loops the combination comprising a source ofsignal energy, a plurality of transformers having their primariesconnected in series to the signal source, a plurality of pairs oftransformers each pair having their primaries connected in series withthe secondary of one of the first mentioned transformers, thesecondaries of each pair being interconnected and having a commongrounded terminal and a pair of supply terminals for connection to thetransmitting loops, and means for selectively grounding each pair ofsupply terminals to ground the loops connected thereto.

30. In a system for selectively supplying energy from a signal source toa plurality of transmitting loops the combination comprising a source ofsignal energy, a plurality of transformers having their primariesconnected in series to the signal source, a plurality of pairs oftransformers each pair having their primaries connected in series withthe secondary of one of the first mentioned transformers, thesecondaries of each pair being interconnected and having a commongrounded terminal and a pair of supply terminals for connection to thetransmitting loops, and means for selectively grounding each pair ofsupply terminals to ground the loops connected thereto, said selectivemeans comprising a switch.

31. In a signaling system the combination comprising a grounded sourceof signal energy, a grounded signal responsive device and a transmissionline comprising a pair of conductors connected together at each endthrough impedances, and means for connecting the signal source and theresponsive device to the respective ends of the transmission line atsubstantially the midpoint of the respective impedances, the portions ofeach impedance being magnetically isolated from each other.

32. A communication system comprising a loop circuit, signal responsivedevices, a physical connection from one terminal of each signalresponsive device to said loop circuit, and a ground connection to theremaining terminal, and series impedances inserted in said circuitbetween said signal responsive devices as a protection against serviceinterruption by open, shunt or ground conditions.

33. A communication system according to claim 32 in which saidimpedances include capacitors.

34. A communication system according to claim 32 in which saidimpedances include resistors.

SEMI J. BEGUN.

